KR20020034162A - Ethylene Acid Copolymer With Enhanced Adhesion - Google Patents

Abstract

The present invention relates to an adhesive useful as a binding layer between a metal foil and a polyethylene film, which is a blend of two ethylene acrylic or methacrylic acid copolymers, one representing a high acid high melt melt index and the other representing a low acid low melt index. It is about.

Description

Ethylene Acid Copolymer With Enhanced Adhesion

Plastic films, in particular polyethylene films, laminated to, coated on or coextruded with metal foil, in particular aluminum foil, have been used in packaging and other products, such as cable shields. The plastic film and the metal foil can be combined with other materials to form a structure having multiple layers of each layer having a specific purpose. For example, packaging stacks often include multiple layers. Such packaging laminates may have a structural rigid core layer of paper or cardboard, a liquid-tight layer of polyethylene, an interlayer of oxygen gas blocking of aluminum foil, and optionally other layers as required by the product. have.

In order to form effective laminates, it is important for most products to achieve good bond strength or tight integrity between layers. In the case of materials that usually do not adhere well to each other, adjacent layers are joined together using an adhesive binder or tie layer.

Low density polyethylene (LDPE) has become a major industry in the foil extrusion coating industry. LDPE is inexpensive, has good workability, and adhesion to metal foil is normal and appropriate in many products. LDPE alone has limitations in the case of products where binding strength persistence, good heat seal properties, and good food adhesion in the presence of aggressive materials are desired.

Ethylene α, β ethylenically unsaturated carboxylic acid copolymers, especially copolymers of optionally partially neutralized ethylene with acrylic acid or methacrylic acid (E / AA and E / MAA) (trade names "Nucrel", "Bynel" and "Surlyn" Available from DuPont Company) in particular binds well to metal foil. Acid groups on these ethylene acid copolymer resins (ACRs) provide a binding site to the basic oxides on the foil surface. As the acid content increases, the adhesion to the foil increases. However, ethylene acid copolymers are more expensive than LDPE and do not bind well with LDPE, especially as the acid content increases.

Thus, there remains a need for an adhesive tie layer that is tightly bonded to polyethylene, in particular LDPE, and metal foil. There is a need to form laminates that are inexpensive compared to foil / ethylene acid copolymer laminates and exhibit excellent persistence of bond strength even in the presence of aggressive materials.

Summary of the Invention

The present invention relates to adhesives, in particular extrudable adhesives, having improved adhesion to both polar substrates such as metal foils and nonpolar substrates such as polyethylene. In particular, the present invention relates to adhesives that provide a bond between polyethylene and a metal foil having persistence in the presence of aggressive substances such as ketchup, flavor oils, juices and the like.

The adhesive of the present invention is a blend of ethylene acid copolymer (ACR) which essentially comprises a high acid high melt melt (MI) acid copolymer and a low acid low-MI acid copolymer.

The invention also relates to laminates comprising a polar substrate, such as a metal foil, and a non-polar substrate, such as a polyethylene film, bonded to each other by the adhesive tie layer of the invention, and to the use of the laminate in packaging and cable shielding products. It is about.

The present invention relates to adhesives, in particular extrudable adhesives, for bonding polar substrates, in particular metal foils such as aluminum foils, to nonpolar substrates, in particular polymer films such as polyethylene films.

As summarized above, the present invention provides a laminate comprising an adhesive, in particular an extrudable adhesive, a polar substrate, in particular a metal foil, such as an aluminum foil, bonded by this adhesive tie layer, and a nonpolar substrate, in particular a polyethylene film, And the use of this laminate.

The laminate of the present invention has a multilayer in which at least one polar substrate is bonded to at least one nonpolar substrate by an adhesive film binding layer.

The thickness of the laminate of the present invention depends on the product and the substrate used. Typical packaging laminates preferably have a thickness of about 0.1 mil (2.5 micrometers) to about 10 mil (250 micrometers), more preferably about 0.5 mil (12.5 micrometers) to about 2 mil (50 micrometers). . The cable shield stack will in fact be thicker than that. Paper substrates will typically be relatively thick (about 1 to about 10 mils (25 to 250 micrometers)), films will be relatively thin (about 0.2 to about 2 mils (5 to 50 micrometers)), and foils typically also Will be thin (about 0.2 to 2 mil (5 to 50 micrometers)).

The nonpolar substrate is preferably a polyethylene film. The polyethylene film may be selected from low density polyethylene (LDPE), linear low density polyethylene (LLDPE) or high density polyethylene (HDPE). Can be prepared by known methods for the preparation of the polyethylene, including high pressure gas, low pressure gas, solution and slurry processes using conventional Ziegler-Natta, metallocene and back transition metal complex catalyst systems have.

The polar substrate is preferably a metal foil, more preferably aluminum foil. Other substrates include metallized substrates such as metallized polypropylene, paper, polyester, nylon, and ethylene vinyl alcohol. Polar substrates may be surface treated by means known in the art, such as corona treatment, to improve adhesion, but such treatments are not necessary in the present invention, and preferably in the case of foil and metallized substrates Do not use.

Prior to applying the adhesive tie layer of the present invention, a variety of primers known in the art, in particular PEI and polyurethane primers, can be used to prime the film substrate.

The adhesive used in the tie layer is a blend of ethylene α, β ethylenically unsaturated C ₃ -C ₈ carboxylic acid copolymer (ACR). In particular, about 5 to about 95 parts by weight of high acid high-MI ACR, preferably about 15 to about 85 parts by weight, more preferably about 15 to about 40 parts by weight and low acid low-MI ACR about 5 to about 95 parts by weight. Blend, comprising about 15 to about 85 parts by weight, more preferably about 60 to about 85 parts by weight. Preferably, the low acid low-MI ACR is the main component and the high acid high-MI ACR is the minor component. At least one is a high acid high-MI ACR, one is a low acid low-MI ACR, and the other copolymer moves to the surface away from the non-polar substrate when the adhesive is coextruded with the non-polar substrate. Two or more ACRs may be included as long as they are incompatible with the high acid high-MI and low acid low-MI ACRs in a manner that prevents them from doing so.

Both high acidic high-MI ACR and low acidic low-MI ACR (as well as other ACRs that may be in the blend) are both ethylene α, β ethylenically unsaturated Cs, optionally having one or more softening comonomers copolymerizable with ethylene. ₃ -C ₈ carboxylic acid copolymer. Acrylic acid and methacrylic acid are preferred acid comonomers. The softening comonomer may be an alkyl acrylate selected from the group consisting of n-propyl-, n-butyl-, i-butyl-, n-octyl-, 2-ethylhexyl-, and 2-methoxyethyl-acrylate. . Preferred alkyl acrylates are n-butyl-, i-butyl-, 2-ethylhexyl-, and 2-methoxyethyl-acrylate. The softening comonomer may also be an alkyl vinyl ether selected from the group consisting of n-butyl-, n-hexyl-, 2-ethylhexyl-, and 2-methoxyhexyl-vinyl ether. Preferred alkyl vinyl ethers are n-butyl vinyl ether and n-hexyl vinyl ether.

Preferably, the high acid high-MI ACR and low acid low-MI ACR are unneutralized. However, as long as the obtained non-neutralized acid content and the melt index of the partially neutralized ACR obtained meet the limits set for the non-neutralized ACR, either or both may be partially neutralized. Preferably, it can be neutralized to a low level by adding cation sources such as zinc, sodium, magnesium and the like. Preferred low levels are less than 500 ppm (more preferably between about 100 and 200 or 300 ppm) based on the total weight of the high acid high-MI ACR and low acid low-MI ACR in the blend.

Useful high acid high-MI ACR and low acid low-MI ACR copolymers are available from DuPont under the trade names NUCREL® and BYNEL®. High acid high-MI ACR and low acid low-MI ACR are described more fully below.

High Acid High-MI ACR

The high acid high-MI ACR is preferably an ethylene acrylic acid or ethylene methacrylic acid copolymer. The acid content and MI need not be absolutely "high", only higher than the acid content of the low acid low-MI ACR and higher than the MI of the low acid low-MI ACR.

Preferably, the% acid of the high acid high-MI ACR is at least 3% by weight greater than the% acid of the low acid low-MI ACR (ie, the acid content of the low acid low-MI ACR is 9% by weight, for example). In this case, the acid content of the highly acidic high-MI ACR will be at least 12% by weight). The difference value is preferably 3 to 15% by weight, more preferably 3 to 6% by weight. The weight percent of acid in the high acidic high-MI ACR is preferably about 7 to about 25 weight percent, more preferably about 10 to about 20 weight percent.

The MI of the high acid high-MI ACR (measured using 2160 gram weight at 190 ° C. according to condition E of ASTM D-1238) should be somewhat larger or greater than the MI of the low acid low-MI ACR. The MI of the high acid high-MI ACR is preferably about 7 to about 1000 g / 10 minutes, more preferably about 10 to about 100 g / 10 minutes or about 10 to about 60 g / 10 minutes.

Low Acid Low-MI ACR

Low acid low-MI ACR is preferably an ethylene acrylic acid or ethylene methacrylic acid copolymer. The acid content need not be absolutely "low", but only lower than the acid content of the high acid high-MI ACR.

The weight percent of acid in the low acidic low-MI ACR is preferably from about 1 to about 22 weight percent, more preferably from about 4 to about 15 weight percent or from about 7 to about 12 weight percent.

The MI of the low acid low-MI ACR should be somewhat smaller or smaller than the MI of the high acid high-MI ACR. MI is preferably from about 0.1 to about 20 g / 10 minutes, more preferably from about 2 to about 14 g / 10 minutes or from about 2 to about 9 g / 10 minutes.

Blend

The high acid high-MI ACR and low acid low-MI ACR are chosen such that the MI of the blend obtained is in a range which can be processed in a coextrusion apparatus, in particular together with LDPE. The MI obtained is preferably about 4 to about 20 g / 10 minutes, more preferably about 6 to about 14 g / 10 minutes. The acid content obtained is preferably more than 1% by weight, preferably at least about 7% by weight, preferably about 7 to about 12% by weight. These% are preferably methacrylic acid equivalents.

Manufacturing Process of Adhesive Bonding Layer

Blends of high acid high-MI ACR and low acid low-MI ACR according to the present invention can be prepared by melt blending the polymer under medium to high shear conditions, for example in a single screw or twin screw extruder. The high acid high-MI ACR and low acid low-MI ACR may first be combined with each other (eg, as a pellet blend) or may be combined with each other by weighing various components simultaneously or separately with an extruder.

Laminate Manufacturing Process

The laminate manufacturing process is preferably a coextrusion coating process well known in the art as described below.

<Procedures used in the examples for the production of laminates>

Laminates were prepared using the coextrusion coating method. Pellet blends of LDPE and ACR (except for this) were injected into separate extruders, melted, combined in a feedblock, and the die pushed out. The foil was contacted with the molten ACR side of the molten extrudate, cooled and wound on a chill roll. In some cases, the foil was corona treated (3.57 watts / ft ² ) to improve the adhesion of ACR to the foil, thereby facilitating separation between ACR and LDPE when measuring adhesion. In all cases, adhesion measurements and acid persistence tests on the foil were performed on untreated structures.

In this example, an LDPE was extruded at about 45 revolutions per minute operation at an outlet temperature of 570 ° F. using a single screw extruder 4.5 inches in diameter and 126 inches in length. The ACR was melt blended in a two-stage single screw extruder, 2.5 inches in diameter and 70 inches in length, at approximately 90 revolutions per minute operation at a temperature profile of 350, 450, 550, 570, 570 ° F. Through a ER-WE-PA feed zone using a Cloeren soft bead reduction die with a 40 inch width (up to 28 inch internal deckle) with a gap of 30 mils and operating at 570 ° F and a back pressure of 260 psig The extrudate from both extruders was combined to form a 0.2 mil thick ACR layer coextruded with a 1 mil thick LDPE layer. This coextrusion was then coated onto a 2 mil thick foil in contact with the ACR side of the extrudate. The air gap between the nip formed by the cold roll and the nip roll (where the extrudate is in contact with the foil) and the die outlet was 7 inches. The chill roll was operated at 60 ° F. The foil line speed was 700 feet / minute.

<Test Used in Example>

Melt Index (MI)

Melt index (MI) was measured by recording the unit of MI value in g / 10 min using 2160 gram weight at 190 ° C. according to condition E of ASTM D-1238. Melt index is a measure of the fluidity of a molten polymer. MI is inversely proportional to viscosity and, in general, the larger the MI, the smaller its molecular weight, depending on the polymer type given.

Acid weight%

The weight percent of acid in the ACR was measured by Fourier Transform Infrared Spectrophotometry (FTIR analysis) using a standard calibrated by titration.

Peel strength

The strip 1 inch wide was cut in the machine direction from near the center of the substrate. The layers were separated at the designated interface (either between LDPE and the acid copolymer or between the acid copolymer and the foil) and pulled in a tensile strength tester at a separation rate of 12 inches / minute at room temperature in the form of "T-peel". The average force required to separate the sample divided by the width was the peel strength (the values in the table were rounded up to almost 10 digits, with "CNS" meaning "not startable", "N / R "means" not operable ". Typically, five separate measurements were averaged together and expressed as values. See ASTM F904. Green peel strength was measured within 4 hours of fabricating the structure. In addition, after one week of storage in a controlled environment, typically at 50% relative humidity, 23 ° C., the peel strength was measured again for the same sample.

Acid persistence test

Several 8 inch by 4.5 inch strips (8 inch dimensions are machine direction) were cut from near the center of the web. Each strip was folded once (with the LDPE side facing inwards) and heat sealed along the side to form a 4 inch by 4.5 inch pouch.

The pouch was filled with 40-45 cm 3 (cc) of 3% acetic acid solution, heat sealed and sealed. Heat seal conditions were typically 290 ° F., 1.5 sec dwell and 30 psig.

The filled pouches were placed in an oven at 40 ° C. The pouch was removed periodically and cut open. The acid was removed and the inner surface was rinsed with water. The pouch was opened and opened in its original form, measuring 8 inches by 4 inches, and three strips of 1 inch wide along the 8 inch length were cut, with each strip having a half top and half bottom separated by fold lines. The bottom half was stored in the oven in constant contact with the liquid. Starting at the bottom of the strip, the polymer coating was separated from the foil (typically at the foil / acid copolymer interface). Peel arms were placed in a jaw of tensile strength tester at room temperature (about 23 ° C.) and pulled at a rate of 10 inches / minute in the form of T-peel. The maximum average force divided by the sample width was recorded as the peel strength. The average of three measurements was recorded.

Based on the recorded data, the acid is the "day to failure", i.e., the day between the filling of the pouch and the day when the pouch begins to inflate or when the peel strength falls below the threshold (typically 200 g / inch). Persistence was recorded.

<Resin Used in Examples>

The acid copolymer resins used in the examples are defined in the table below.

<Examples C1, 2 and 3>

As can be seen in the table below, the blend of high acid high-MI ACR and low acid low-MI ACR showed better performance than single ACR with the same acid content in the peel test. The data illustrate three ACRs in the blend of the present invention.

<Examples C4, 5 and C6>

As can be seen in the table below, in the peel test, blends in which the MI of the high acid ACR was higher than the MI of the low acid ACR showed better performance than blends in which the MI of the high acid ACR was smaller than the MI of the low acid ACR.

<Examples C7, 8 and C9>

As can be seen in the table below, in the peel test, blends with lower total acid content than single ACR could show better adhesion performance than high acid single ACR.

<Examples C10, 11, C12 and 13>

In the following examples using ethylene acrylic acid copolymer resin, the blend of high acidic high-MI ACR and low acidic low-MI ACR in the peel test showed superior performance compared to single ACR with higher acid content.

<Examples 14, 15, 16, 17, 18 and 19>

As can be seen below, the melt blend and pellet blend in the peel test showed similar results.

<Examples C20, 21, C22 and 23>

As can be seen in the table below, Example 21 has a lower total acid content but greater peel strength to foil, better adhesion to LDPE and longer lasting in aggressive acidic environments than Example C22. . Example 23, which had a similar acid content but lower acid content than C22, had greater peel strength, better bond persistence, and better adhesion to LDPE than Example C22. .

While not intending to limit the invention, it is believed that improved binding persistence may be due to the highly acidic high-MI ACR that forms the foil / ACR interface. However, the binding persistence was lower than expected (> 20 days) at pure 15% acid grade. Since the higher the acidity of the copolymer, the greater the resistance to acid migration, this may be due to the polymer's resistance to acid diffusion at the ACR / foil interface. This suggests that the bond persistence is related to the functionality of the acid at the foil / ACR interface (the number of chemical bonds formed between the acid on the polymer and the oxide on the foil surface) and the polymer's resistance to acid diffusion at the interface.

<Examples C24, 25, C26 and 27>

Days to failure were recorded as ranges in these examples to reflect different results from repeat tests. Example 25 had a lower total acid content than Example C26, but not only better peel strength for aluminum foil, but also better bond persistence in the presence of acetic acid. Example 27, which exemplified low acidic low-MI ACR as a minor component in the blend, had better peel strength for LDPE and nearly identical bond persistence compared to Example C26.

Claims (15)

At least one ethylene-α, β ethylenically unsaturated C ₃ -C ₈ carboxylic acid copolymer containing about 5 to about 95 parts by weight of high acid high-MI ACR and about 5 to about 95 parts by weight of low acid low-MI ACR (ACR) blends, a. The high acidic high-MI ACR has an acid content of at least 3% greater than the acid content of low acidic low-MI ACR and is measured using MI (2160 gram weight at 190 ° C according to condition E of ASTM D-1238). ) Is an ethylene α, β ethylenically unsaturated C ₃ -C ₈ carboxylic acid copolymer that is greater than the MI of the low acid low-MI ACR, b. The low acid low-MI ACR has an acid content of about 1 to about 22 weight percent and a MI (measured using 2160 gram weight at 190 ° C. according to condition E of ASTM D-1238) of about 0.1 to about 20 g. / 10 minutes Except c. The MI of the blend obtained is about 4 to about 20 g / 10 minutes, Adhesive for bonding a non-polar substrate coextruded with an adhesive to a polar substrate. The adhesive of claim 1 wherein the acid content of the high acidic high-MI ACR is about 3 to about 15% greater than the acid content of the low acidic low-MI ACR. The adhesive of claim 1 wherein the acid content of the high acidic high-MI ACR is about 3 to about 6% greater than the acid content of the low acidic low-MI ACR. 4. The adhesive of any one of claims 1, 2 and 3 wherein the MI of the highly acidic high-MI ACR is about 7 to about 1000 g / 10 minutes. The adhesive of claim 4 wherein the MI of said highly acidic high-MI ACR is from about 10 to about 100 g / 10 minutes. The adhesive of claim 5 wherein the high acidity high-MI ACR has a MI of about 10 to about 60 g / 10 minutes. The adhesive of claim 1, wherein the blend has from about 15 to about 85 parts by weight of the high acid high-MI ACR and from about 15 to about 85 parts by weight of the low acid low-MI ACR. . 8. The adhesive of claim 7, wherein the blend has about 15 to about 40 parts by weight of high acid high-MI ACR and about 60 to about 85 parts by weight of low acid low-MI ACR. The adhesive according to any one of claims 1, 2 and 3, wherein the low acid low-MI ACR is the main component of the blend. 4. The adhesive of any one of claims 1, 2 and 3 wherein the acid content of the blend is about 7-12 wt%. A laminate comprising a multilayer of at least one polar substrate and at least one layer of nonpolar substrate, to which the polar substrate is bonded to the nonpolar substrate by the adhesive layer of any one of claims 1, 2 and 3. The laminate of claim 11, wherein the nonpolar substrate is a polyethylene film and the polar substrate is a metal foil. The laminate of claim 12, wherein the metal foil is aluminum foil. The method of claim 1, comprising coextruding the adhesive of claim 1 with the nonpolar substrate and coating the obtained extrudate on the polar substrate in a manner such that the adhesive layer is in contact with the polar substrate. And a polar substrate and a nonpolar substrate. The method of claim 13, wherein the polar substrate is polyethylene and the nonpolar substrate is a metal foil.